1. Field of the Invention
The present invention relates to dechlorination of polychlorinated aromatic compounds that are environmental pollutants. More particularly, the present invention relates to a method of treating polychlorobiphenyl contained in a hydrocarbon oil, especially in an insulating oil used in a transformer.
The present invention also relates to a method of treating a polychlorinated aromatic compound which is advantageous by antipollution considerations. This method allows the removal of chlorine from polychlorobiphenyl contained in an insulating oil. The resultant reaction product is thus an organic compound with no chlorine content, and may be disposed of as an industrial waste and a municipal waste. In addition, the oil after treatment may be recycled as a harmless hydrocarbon oil.
2. Description of the Prior Art
Polychlorinated aromatic compounds such as polychlorobiphenyl (PCB) are known as environmental pollutants. Such compounds are contained in, for example, insulating (hydrocarbon) oils used in a transformer. The insulating oil polluted with the polychlorinated aromatic compound is recovered and stored under present technical conditions.
Some articles disclose the decomposition of PCB by means of heating the composition (such as oil) containing PCB at a high temperature. This method, however, requires special facilities and some supplementary facilities to generate a high temperature. Such facilities may also be required to purify the exhaust gas because there is a possibility of causing incomplete decomposition of PCB. Alternatively, the polychlorinated aromatic compound, such as PCB-contained in the hydrocarbon oils may be removed therefrom through chemical decomposition. In this method, the hydrocarbon oil is stirred while heating along with polyethylene glycol and an alkali metal hydroxide. This technique is disclosed in, for example, Japanese Patent Laid-Open Nos. 49-126651 and 60-114278.
It is known that the chlorine of PCB in these methods remains in the polyethylene glycol layer as a reaction product which has a bound chlorine (organic chlorine compound) rather than being removed completely.
In other words, it is only possible to remove PCB from the hydrocarbon oil but another problem occurs on disposal of the organic chlorine compound remained in the polyethylene glycol layer. In addition, typical chemical methods of removing PCB require a solvent or solvents added to the composition from which PCB is to be removed for decomposing the latter. This means that the treating process becomes complicated due to the necessary steps of separating and recovering the hydrocarbon oil and the solvent after the reaction, and of treating the used solvent.
As mentioned above, the known methods are insufficient by practical considerations because PCB is not completely dechlorinated, even by using the specific facilities and/or complicated treating process.
Accordingly, an object of the present invention is to provide a safe, effective method of dechlorinating polychlorinated aromatic compounds that are environmental pollutants.
Another object of the present invention is to provide a method of removing polychlorobiphenyl contained in a hydrocarbon oil, especially in an insulating oil used in a transformer.
Yet another object of the present invention is to provide a method of removing chlorine from polychlorobiphenyl to achieve complete removal of an organic chlorine compound from the entire system after reaction.